When hydrochloric aicd is addded to cobalt and nitrate solution at room temperautre, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the corect ansewer.
`underset("pink")[[Co(H_(2)O)_(6)]]^(3+)(aq)+4CI^(-)hArr`
`underset("blue")[CoCI_(4)]^(2-)(aq)+6H_(2)O(l)`

Options

A. `DeltaH gt0 ` for the reaction
B. `DeltaH lt0 ` for the reaction
C. `DeltaH =0 ` for the reaction
D. The sign of `DeltaH `cannot be predicted on the basis of this information

Answer

A

Explanation

In the reaction, `underset(("Pink"))([Co(H_2O)_(6)]^(3+))(aq) +4Cl^(-) (aq) hArr underset(("Blue"))([CoCl_4]^(2-))(aq)+6H_2O(l)`
On cooling, the equilibrium shifts backward direction or on heating, the equilibrium shifts forward direction.
Hence, reaction is endothermic. i.e., `DeltaH gt 0`